Time-multiplex pulse-code modulation signal transmission system



May 8, 1956 J. A. GREEFKES ETAL 2,744,960

TIME-MULTIPLEX PULSE-CODE MoDuLATIoN SIGNAL-TRANSMISSION SYSTEM Filed May 9. 1951 I 5 Sheets-sheet 1 I l I l l AsA J l l I I I I E703 JOHANNES ANTON GREEFKES PIETk VAN TILBURG AGENT May 8, 1956 J. A. GREEFKES ET AL 2,744,960

TIME-MULTIPLEX PULSE-CODE MODULATION SIGNAL-TRANSMISSION SYSTEM 3 Sheets-Sheet 2 Filed May 9, 1951 FFT TNVENTORS l `JOHANNES ANTON GREEFKES PIET VAN TILBURG May 8, 1956 J. A. GREEFKES E-r Ax. 2,744,960

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lN'vENToRs `JOHANNES ANTON GREEFKES PIET VAN mBURG BY AGENT United Statesv Patent O Johannes `Anton Greefkes. and Piet yan Tilburg, ihov'en, Netherlands, ssglll'ofrsftb 'Harttrml National Bank and Trust Company, Hartford, Conn., as trustee Application Mays, 19511-, 'seal Nn. 225,314 Claims prim/ity,ap':plic'tiaa Nethnuls time '23, i950 7 claims. (ctms- 15) This invention relates to arrangements vfor regenerating in form and relative time 'of occurrence and lfor distributing in cyclicy sequence signal-pulses from trains of signal-pulses, which trains are each vpreceded by'a synchronisation pulse, at Ithe receiving lendort a time-multiplex `pulse-code modulation signal-'transmission system,

the signal-pulses being alternatively present or absent in accordance with the signals to be transmitted.

'Characteristic of such pulse-code modulation systems is inter alia the use of time quantising, i. e., at the transmitting end 'there are transmitted only puls'esvycoinci ng vwith pulses ota train of equispaced pulses, This 'permits at the 'receiving end 'practically complete eliinination of transmission faults introduced by displacementsin time of I,the input pulses, by means of tpulse generators preceded, if desired, by arnl'alitude threshold devices a'nd amplitude limiting devices. s y l y e In order to regenerate incoming pulses, 'it 'is k'noyvn to use at the receiver a 'local pulse generator 'producing pulse's of a -recurrence frequency Which, by automatic frequency correction, is maintained equal to 'the average maximum recurrence frequency of the Vincoming pulses. The pulses thus produced locally are supplied to a coincidence mixer stage to which the incoming pulses', if 'desired aftel being lengthened, kare also supplied. This coincidence mixer stage transmitsuthe pulses or `substitution ,pulses locally produced only if they coincide With Iil 1c 'orn ing pulses. Hence, pulses corrected in time ofocczu'rrnce replace the incoming pulses and a better sighalfto-noise ratio is obtained, 'I-Iowever,` troublesome cross-'talk may occur in such multiplex receivers i w s The present invention has `ornits object to provide an improved arrangement for use intime multiplex pulsecode modulation signal transmission systems in fWhich crossftalkebe'tween Vthe :time multiplex channels is fnaterially reduced. y y l y y ,i According to the invention, an arrangement for regenerating in ytorn/l and time of occurrence and distributing in cyclic sequence signal-pulses from` trains of signalpulses, which trains are each preceded by arsynchronisation pulse, at the receiving end of a time-multiplex pulsecode modulation signal-transmission System, the signal pulses being alternatively present or absent inhacco'rdance with the signals to be transmitted,pharaeterize in 'that the incoming pulses are supplied by Way of a synchronisation pulse selector to `a synchronisation 'pulse lfegenerator, the output of which is coupled to the input of va 'first delay network, the arrangement 'comprisingindividual receiving channels each including a first'coincidence 'mixer stage to which first coincidence mixer stages signal pulses to be regeneratedI are supplied, a'n'd inputs of the said lli'st coincidence 'lni'xer stages moreover being connected each individually to different tapping points of the first delay network for the supply of substitution pulses, andthe separated and regenerated signal pulses being taken from the output circuits ofthe firsty coincidence mixer stages. In connection with the distribution of the signal pulses among the individual `receiving channels in this arrangeratorshould lbe.4 less than vone 1-signal interval.

channels are preferably'supplied to each"li/rstV Amixer stage `th'r`ou-gll fa;v econo coincidencei fm -toQyvliich second coincidence, l'nixeri Vsurges the'ln pulses are suppliedin parallel, 'iplits'offtlie Asec 2,744,960 Patented May 8,7.1956

ment, the variation `of tlepliasejuispiameiit between the synchronisation pulsesl occurring'atthe input of 'the 'synchronisation pulse selector andthe 's'ubstantiallyinoisefree pulses taken frorn the synchronisation plilse regener- To reduce the ,string cfy Yof this o i K v A l requitentent it is dilllcultto fulflliin practice, the `s gnal pulses'tofbe regenerated `and occlurring'in the individual.

coincidence "mixer :stages alie inflation 'with a simple, automatically entre 'ed p corrector, even ifv a comparatively great variation Jofftl'e recurrence frequency of the`synchronsation 'pulses yls to be 'allovved for at thetransmitting end.

`In k,order that the linvention may be readily, 'carried into effect, it Will now be 'described in greater detail with 'reference to the accompanying diagrammatic drawings, .given by wayjoffexample, irl lwhich: A

A Fig. l isa tmefdl grarnof ylzvillses produced lbyjaf9ll charl'nelfti'rne multiplex transmitter inv a system oflltlie aforesaid type used in signal "transmission by ineans of'a one unit code (so-called quan,tuin-ri'lodulation),y

Fig'. 2 isa block diagranl of l'a receiver compris y 'A' rrange'ment according 'to the invention for receiving the .pulse Itrains`sho'\`yvrl.,i'l1 `Fig. l,

Fig. 3 is a block diagram "l anjimrQ/e'd fece' `er comprisingHanarrangemelit according to theeinventlom Fig. 4 shovvsia synchronisation pulse "selector lfor use in the leceive'rfshownfinFig. l2 or 3,VVT

The tiine 'diagram represented, Such trains olifsignal pulses for signally'tdranslnissionyyvith jqllaii'turninodulation 4may be produced er signal channel with the .u'seof `the transmittersdescr' ed in U. s, vlutttit No. 2,662,118, issuedneiab ,8,y 195.3, and in S.patent application Serial No. 2id-4%; filed Marnz'o, l1,951. s i

In yLrlelatioll 1to shape,rduratiol1and amplitudegtliereis no difference betiveer'l the signal pulses {and} theV synchroni'sation pulses. The synchronisation pulses are distinguished by their continuous presence, i. `e., each signal cycle compifises a. synchronisation pulse during-:the :time interval designated li.; Pulses of,aparticular signahclib nel are alterntivelypresent or, absentin accordance with' thesignal to be transmitted throughthe channel in question. L 1 f Fig.' l will, after transmission, be shaped as shown in the time diagram of Fig. 7a, where not only the amplitude and the shape of the pulses but also their relative spacing is different. This may be seen at the receiver since the in- -coming pulses exceed a given threshold value Vd at nonyequispaced instants. Reduction of the noise caused by 'mutilation and time displacement of the pulses requires fspecial steps to be taken at the receiver end.

Fig. 2 shows a simple receiver, for receiving pulse trains as shown in Fig. 7a, in which the pulses picked up by an aerial 10 are supplied to an amplification stage 11 which may successively comprise a high-frequency amplifier, a mixer stage, an intermediate-frequency amplifier, an amplitude detector and an amplitude limiting and threshold arrangement. The pulses taken from the detector lhavea shape as shown in Fig. 7a and, after passing through the threshold arrangement and the limiter approximately at the level designated Vd in Fig. 7a, they have a shape as shown in Fig. 7b. All the pulses shown in Fig. 7b have the same amplitude, but their leading edges are not equispaced and the duration of all the pulses is not equal. The signal and synchronisation pulses taken from the amplification stage 11 are supplied to a synchronisation pulse selector 12, one construction of which will be described with reference to Fig. 4. In the output circuit of the synchronisation pulse selector 12 only the synchronisation pulses of Fig. 7b occur; they are shown in Fig. 7c. The synchronisation pulse selector is preferably such that all the pulses taken therefrom are of the same duration. Due to interference, however, their relative times of occurrence are not such that they are equispaced.

In order to mitigate this drawback which causes noise in the incoming signals, the selected synchronisation pulses are supplied to a synchronization pulse regenerator, or noise suppressing device 13, of which only the block diagram is shown in Fig. 2. As a possible detailed construction reference is made to the description thereof in U. S.

Patent No. 2,662,118, issued December 8, 1953.

The noise suppressingdevice comprises a local oscillator 14 which supplies a sinusoidal oscillation and is tuned to a frequency corresponding substantially to the recurrence frequency of the incoming synchronisation pulses. The sinusodial oscillation of oscillator 14, together with the synchronisation pulses occurring at the output of the synchronisation pulse selector 12, is supplied to a phase detector consisting of a mixer stage 15. Across the output circuit of this mixer stage a control direct voltage is set up, which depends upon the phase of the synchronisation pulses in relation to the sinusoidal oscillation. After having been smoothed by means of a low-pass filter 16, the said control direct voltage controls a reactance tube 17 coupled to the frequency-determining circuit of oscillator 14. In this manner the frequency and phase of the local oscillator 14 are automatically stabilized on the recurrence frequency of the synchronisation pulses. The synchronisation pulses supplied to the regenerator 13 exhibit considerable phase variations, but these will not occur, or at least be materially reduced, in the sinusodal output voltage of oscillator 14, provided the time constant of the smoothing filter 16 be given a sucient value, for example such that the cut-off frequency is at the most M00 to 1/600 of the recurrence frequency of the synchronisation pulses. The sinusoidal oscillation of oscillator 14 thus being comparatively stable in phase is supplied through an amplitude limiting and threshold arrangement 18 (slicer) to a differentiating network 19, the output circuit of which comprises a series-connected diode and a parallel resistance for suppressing pulses of negative polarity. In the output circuit of the differentiating network 19 then occur pulses of positive polarity and of a recurrence frequency substantially accurately corresponding to the average recurrence frequency of the incoming synchronisation pulses, but, as distinguished from the lastmentioned pulses, substantially without time-displacement noise.

The pulses obtained are utilised for replacing the incoming signal pulses and are supplied by way of a lead 20, to a delay cable 21, to different tapping points of which are connected first coincidence mixer stages located in the individual receiving channels A1 to A9. The receiving channels A1 to A9 are similar. Only the coincidence mixer stage of channel A1 is shown in the block diagram thereof and denoted 22. To the coincidence mixer stage 22 are moreover supplied all incoming pulses, if desired after convenient lengthening, which occur at the output of amplification stage 11. In the output circuit of mixer stage 22 pulses occur only if at the mixer stage 22 an incoming pulse and a substitution pulse taken from the delay cable 21 coincide. Due to interference in the transmission path, the incoming pulses were different in relation to amplitude, duration and shape and, moreover, displaced in time of occurrence, but the pulses set up in the output circuit of coincidence mixer stage 22 substantially no longer suffer from these transmission faults. Moreover, by a suitable choice of the tapping from the delay cable 21, there will occur only those signal pulses in the output circuit of mixer stage 22 in channel A1 of the signal interval designated 1 in Figs. l and 7. During the remaining signal intervals, no substitution pulses are supplied through the delay cable 21 to the mixer stage 22. Hence, the latter cannot supply output pulses, so that the aforesaid means also effect the distribution of the signal pulses between the individual receiving channels A1 to A9.

The pulses of the time intervals 1 occurring in the output circuit of coincidence mixer stage 22 are supplied, through a pulse Widener 23, to a signal frequencies integrating network 24, across the output circuit of which the transmitted signal occurs. In order to remove the pulse recurrence frequency and higher harmonics thereof, the output signal of the integrating network 24 is supplied to a loudspeaker 26 through a low-pass filter 25 and, if desired, through an amplifier.

In this respect it is to be noted that for noise-elimination in a proposed pulse-code modulation receiver, all incoming pulses were supplied to a regenerator similar to that shown at 13, which was tuned to the maximum recurrence frequency (500 kos/sec. in Fig. l) of the incoming pulses. Since the incoming pulses per channel are alternatively present and absent in accordance with the signals to be transmitted, the control voltage produced in the regenerator 13 then comprises signal voltage components and consequently troublesome cross-talk through the noise-suppression device. In the receiver shown in Fig. 2, such cross-talk can substantially not be introduced by the regenerator 13, since the signal pulses are not supplied thereto. Cross-talk could still occur if, for example due to parasitic reflections or the like, band width limitations, damping phenomena in oscillatory circuits and so on, the trailing edges of the signal pulses were to extend into theV synchronisation interval. By a suitable construction of the apparatus, this cross-talk, which` decreases with the time spacing between the synchronisation interval and a preceding signal interval, can easily be reduced to a permissible value.

In the receir'cr shown in Fig. 2, the variation of the phase displacement between the pulses supplied to the regenerator 13 and the regenerated pulses derived therefrom should remain smaller than approximately 1/i of a signal interval. A greater variation of this phase displacement Would cause pulses, for example intended for signal channel A2, to reach the immediately preceding A:metuse channel A1 :or ythe next succeeding clrlanrnel '.iAs. :lniprractice, :it'is objectionable `f'to einaintainsuchf afsmall ftlerance Withfr'espectto thephase displacementin zthe'regenerator 13, notably if the `recurrence frequency yof Vthe synchronisation pulses is not maintained perfectly constant'at the transmitter.

These difficulties lmay -be further freduced "with 'fthe receivershown inFig. 3.

ln Fig. 3, the lincoming pulseszpicked'up:ibyithe'aerial are yagain supplied, by way of the amplification vvstage y1-1 .comprising inter .alia a detector, do the '-synchronisation -pulse selector 12. The `selected synchronisation pulses ycontrol `a regenerator 27, ithede'tailsof which will be .described with reference to Fig. 5. '["ne'regenerated pulses occurring in the 'output lead '20 are supplied, to 1a ir-stdelay cable 2l, sultabletappingpoints of -which Vare connectedto the Linputs'of :first `coincidence mixer stages located fin vthe individual, 'similar receiving channels A1 to A9 respectively. "Of 'thesefcoincidence -miXer stages only thes'tage -denoted 28 of 'signal channel A3 is `shown in any detail. The output pulses of "the coincidence mixer stage 28 are supplied 1o anintegrating network '29 and the signal voltage obtained vtherefrom is supplied to a loudspeaker 31 by Way of a loW-passtjlter 30.

`Besides 'the pulses taken from `the delay (cable 21, further ypulses Iderived from the incoming pulses 'are supplied to the rst coincidence mixerfstage 23. Synclnconisation pulses occurring 1in the output circuit xof 'selector 12 .are supplied to a second delay cable '32,10 'suitable tapping points of which are connected second 'coincidence mixer stages. for example 33 in vchannel A3, situated in the individual receiving channels. Moreover, all incoming pulses are supplied'in parallel connection toiinputs of the said second coincidence'mixer stages, Ibut-'thesesecond coincidence mixer stages supply output pulses only if a pulse supplied thereto through the second delay cable 32 ycoincides with an incoming pulse. Consequently, the secondcoincidence mixer stages eiect the distribution of the signal pulses received in ytime-division multiplex between the individual receiving channels A1 'to A9. The output pulses of the ysecond coincidence 'mixer `stages 33 are supplied by Way of a pulse expander 34 1to an input of 'the lirst coincidence mixer stage 23.

Fig. 4 is a 'more detailed diagram of a synchronisation pulse selector which it is preferred 'to use lin the receivers 'Shown in Figs. 2 and 3,-which selector Ais denoted 12 in `Figs. 2 and 3. it is assumed that -pulses similar to those shown 'in Fig. 7b are supplied to -the `said seledtor. The synchronisation pulses areshaded 'in Fig. 7b. The pulses supplied to the selector lare assumed to l'be of negative polarity.`

The selectorshow-n in Fig. 4 comprises .a tiiggercircuit including two pento'des 35, 36 having 'a `common cathode resistor 37. The control grid of pentode 35 'is connected to the end, remote from 'the cathode, of cathode resistor 37, so that vit has a high-negative 'bia'sj The Acontrol grid fo'f pentode 35 is connected by way of a grid fresis'tor -33 to the 'anode voltage lead 39 (for example, +250 volts) 'and lto the anode of a grid voltage limiting diode 40, the fc'athode of which is 'connected to a variable voltage 'divider comprising resistors `41 and 42 and being connected 'between the earth lead 43 `and the anode voltage lead 39. The control grid of pentode '36 normally has a potential 'substantially corresponding -to the potential of the assofciated cathode. Since the control grid 'of pentode 35 is highly biassed negatively, the pentode 36 will normally be conductive and-'pentode 3S `will be cut ott. In this state of equilibrium of 4the 'trigger circuit, the anode of `pen'tode 35 is at a high positive potential, with the result that a diode connected thereto 'is conductive land the cathode of which diode is maintained Vat a suitable positive potential by means of a voltage divider arranged in A'parallel with 'the source ot anode voltage and comprising a resistor 46 and a glo'w discharge 'tube 47. Thercathode ff 'the diode '45 is connected vthrough 'a resistor V48 .to a

tapping "(-\for, example-"approximately `l5() volts) of the last-mentionedvvoltage divider. Y p

In the aforesaid state of eqt 'brium of the trigger circuit, incoming pulses of negative polarity supplied to input terminals 49 will be supplied fto `the controlgrid of pentode 36 through the diode 45 vand acoupling capacitor 50 located between the ranode of pentode '35 and the control -grid of gpentode 36,` with the result 'that vpentode 36 is cut voff and pentode 35 becomes conductive. Owing to the pentode 35 becoming conductive, its 'anode Vacquires a low positive potential such thatthe diode 45 connected to this anode is cut oli and Afurther impulses supplied yto the input 'terminals cannotinluence the -crosswise coupled pentodes 35 and 36. l

After av lapse of time dependent upon thejtime4 constant of the trigger-circuit including pentodes 35 and 36, the circuit will Hip vback into -its initial :stateof equilibrium, in which the pentode 36 is conductive and -pentode 35 is cut oft. On nipping back into this initialstate of equilibrium, the diode 45 becomes conductive so that a next following incoming pulse` will cause the trigger circuit to respond. The time constant of the trigger circuit is chosen such that, after having responded yto an incoming. pulse, it remains insentitive during a time smaller thanone signal cycle, for example T1, and greater than this signal cycle less `one signal interval. lf the trigger circuit in the signal interval T1 shown in Fig. ll were to respond, for example, to the signal `pulse in the interval 3 it will remain insensitive lup ,-to just before the occurrence of the signal pulse in the time interval 8, of signalcycle Tz-and will subsequently respond to a signal pulse 8 present in the signal cycle T2. The selector will now again become insensitive upto just before the interval 8 of signal cycle T3, out in this case it cannot respond during this interval 8 owing tothe absence of the signal pulse in question, due to whichf'the trigger circuit then responds to the signal pulse of interval 9 in signal cycle T3. Vln this event, the circuit arrangement remains responsive to 'pulses in 'the signal interval '9 until this pulse also is once absent, whereupon i-t responds to the synchronis'ation pulses from interval 6 of the signal cycles. Since, as stated above, the synchronisation pulses occur in each signal cycle, the circuit arrangement will subsequently remain responsive to these synchronisationpulses, so that the trigger circuit comprising pentodes 35, 36 will flip over whenever a synchronisation pulse is received. ln this manner 'the synchronisation pulses are selected. vEach time the pentode 36 is cut oft by a synchronisation pulse, a voltage pulse occurs in the `anode circuit of this pentode, thus shock-exciting an oscillatory circuit lincluding a'coil 51, a capacitor 52 and an attenuation resistor S3 located in the anode circuit thereof. v The said oscillatory circuit imparts by way of coupling capacitor y54 ,a positive voltage pulse of a duration determined by the natural frequency of the oscillatory circuit 51, 52 to the l control grid of a pentode ampli'er 55 which is normally cut oit by a'negative grid bias taken from a voltage divider 56 connected between the earth lead 43 and a negative voltage lead 44. The anode lead of pentode comprises an output transformer y57, a vdiode,58V being connected in parallel with the secondary windingthereof t0 suppress Apulses ofk negative polarity. Consequently, va positive pulse of particular `duration coinciding with ,the synchronisation pulses of Fig. 7b, voccurs at output terminals 59,l connected to the secondary winding of the output transformer 57, on reception of e'ach 'synchronisation pulse. The synchronisation pulses thusselected areshown in the time diagram of Fig. 7c.

Fig. 5 represents a synchronisation pulse regenerato'r which it is preferred to use in the receiver lshown in Fig. 3. Herein, the synchronisation pulses occurring lat the outputterminals 59 (Fig. 4) of the synchronisation pulse selector, are supplied to yinput terminals 60 of an input transformer 61. To the sccondarywinding of `this input trnsfonner is connected a filter network ofla type known per se, which comprises four'crystals 62 and is tuned to the recurrence frequency of the synchronisation pulses. The output circuit of the said lter network includes a transformer 63.

When the selected synchronisation pulses shown in Fig. 7c are supplied to crystal lter 62, a sinusoidal voltage as shown in Fig. 7d will be set up across the output circuit of the said lter, the phase of this voltage will, provided the lter has a high Q (for 'example 500 to 1000, as is readily attainable with crystals, vary only very slightly with the instantaneous phase of the fundamental frequency of the synchronisation pulses supplied. Owing to the use of the high grade crystal filter, thc phase of the sinusoidal output voltage of the lter will be determined by the phase of the input pulses, averaged over, say, at least 500 cycles of the recurrence frequency of the input pulses. Consequently, the phase of the input pulses in cycles immediately succeeding each other will be subject to variations due to interference in thc transmission path, but these phase variations occur strongly attenuated in the output circuit of the crystal ltcr.

The secondary winding of transformer 63, across which the sinusoidal oscillation of Fig. 7d occurs, is connected in the control-grid circuit of a pentode 64 having an anode circuit 65 tuned to the frequency of the sinusoidal oscillation. The anode circuit 65 comprises a capacitor 66 and an iron-cored coil 67 having a self-inductance which depends upon the anode current of pentode 64 and is utilised for readjusting the tuning frequency of the anode circuit 65 in order to establish a particular desired phase relationship between the grid and anode alternating voltage of pentode 64.

To convert the anode alternating voltage of pentode 64 into a substantially rectangular voltage, it is supplied to a trigger circuit (Slicer) of a type known per se comprising two cross-coupled triodes 67, 68.

The triodes 67, 68 have a common cathode resistor 69 and anode resistors 70 and 7l., respectively. Through a germanium cell 72 the control grid of triode 6'7 is connected to the earthed end of cathode resistor 69, a negative bias being applied to the control grid of triode 68 by way of a germanium cell 73. A coupling capacitor 74 is connected between the anode of triode 67 and the control grid of triode 68.

As is known, the trigger circuit described has the property that a sinusoidal alternating voltage supplied thereto through an input capacitor '7S is sliced. In accordance with the potential impressed on the input control grid, the trigger circuit assumes one or the other of two states of equilibrium. At an input potential eX- ceeding a particular value, the triode 67 is conductive and triode 68 is cut off. At a lower potential of the input control grid, the trigger circuit is in the other state of equilibrium, wherein triode 67 is off and triode 68 is conductive. With the use of germanium cells in the triode control grid circuits, the working point of the trigger circuit adjusts itself automatically to a suitable value, the

limiting potentials being only slightly ditterent.

When supplying a sinusoidal voltage to the input control grid of the trigger circuit the triode 68 is alternately cut o and conductive, so that a voltage of the shape depicted in Fig-7e is set up across the anode resistor 71 of the triode 68. The substantially rectangular voltage is supplied through a differentiating network comprising a capacitor 76 and a resistor 77 to the control grid of a pentode 78 which, by connecting the control grid through a grid resistor 79 to a negative source of grid bias, is biassed such that the pentode 78 is normally cut off. At the output resistor 77 of the dilerentiating network 76, 77 positive and negative pulses alternately occur, as shown in Fig. 7f, of which only the positive pulses (shaded in Fig. 7f) cause anode current to flow in the pentode 78. The anode circuit of pentode 78 comprises an output transformer .-80. Each'time a pulse of positive polarity is supplied to the control grid Aof the pentode 7S, a positive and a negative pulse occur across the secondary winding of the output transformer 80, the negative pulse being suppressed by a rectier cell 81, so that pulses of positive polarity occur at output terminals 82 connected to the secondary winding.

As stated above, the variations of phase displacement between input and output pulses of the synchronisation pulse regenerator should not be excessive in connection with the practical construction of the receiver shown in Fig. 3. It allowance must be made for relative variation of the recurrence frequency, fixed at the transmitter, of the synchronisation pulses and the tuning frequency of the crystal filter 62 in the synchronisation pulse regenerator of the receiver (Figs. 5 and 3), the said phase variations between the input and output pulses of the synchronisation pulse regenerator should be prevented from attaining an excessive value due to the high selectivity of crystal lter 62. This is ensured by providing the synchronisation pulse regenerator shown in Fig. 5 with means for automatic phase-correction of the output pulses in relation to the input pulses. To this end the input pulses occurring at the output terminals 82 are supplied by way of a coupling capacitor to the control grid of a pentode 83 with an integrating network 84 included in the anode circuit. The pentode 83 is normally cut off by connecting the control grid to a tapping of a voltage divider comprising'resistors 85, 86 and being connected in parallel with a source of negative grid bias. Whenever a positive pulse is supplied to the pentode 83, an anode current pulse occurs therein with the result that a capacitor 87 of the integrating network 84 is charged. Between succeeding pulses, the pentode 83 is cut oit and the charge of integration capacitor 87 decreases gradually. The time constant of the integrating network 34 is so chosen that the integration capacitor 87 is only partially discharged between two succeeding input pulses of pentode 83. In this manner a sawtooth voltage having a fundamental frequency corresponding to the recurrence frequency of the pulses supplied to pentode 78 is set up across the integrating network 84.

The sawtooth voltage set up at the anode of pentode 83 is supplied, by way of a coupling capacitor 88 and a decoupling resistor 89, to an input resistor 90 of a circuit comprising a diode 91 and acting as a peak detector. The input pulses to input terminal 60 supplied to the synchronisation pulse regenerator are supplied to the input resistor 90 of the detector circuit through a coupling capacitor 92 and a decoupling resistor 93. In order to bias the detector circuit, the input resistor 90 is connected through a resistor 94 to the negative terminal 95 of a source of grid bias.

Across the input resistor 90 of the detector circuit the sawtooth voltage from the integrating network 84 and the input pulses of the regenerator are added, so that a voltage dependent upon the phase-relation of sum voltage set up across the input resistor 90 appears in the output circuit of the detector. The output circuit of the detector comprises a low-pass lilter with series-resistors 96, 97 and parallel capacitors 98 and 99, the latter being shuntedy by a resistor l100. The output voltage of the detector circuit has a positive polarity and is supplied through a resistor 101 to the control grid circuit of pentode 64, together with a negative grid bias supplied thereto through a variable resistor 102, owing to which the total grid bias of pentode 64 depends upon the phase relation existing between the input and output pulses of the synchronisation pulse regenerator. Upon a variation of the phase relation of input and output pulses, the grid bias of pentode 64 and consequently its anode current and the tuning of anode circuit vary such that the said phase variation is counteracted and a particular desired phase relation between input and output pulses of the regenerator can be accurately maintained to within a few degrees. The desired phase relation can be adjusted by adjustment of resistor 102 in the grid circuit of pentode @pagina f the synchronisation pulse selector 12. rThe "pulses taken from the `synchronisation pulse selectorare shown'in Fig. 7c, the pulses obtained therefrom after retardation and supplied 'to input terminal 103 areshown shaded in Fig. 7g. Through a coupling capacitor 104 these-'pulses are supplied to the vcontrol grid of a pentode 105 lwhich yis used as a coincidence mixerfstage and is-no'rmally cutoff by a suitable bias. The control grid'circuit furthermore comprises a variablep'arallel 'capacitor 106 in order that the capacity occurring between the input terminal 103 and earth may be adjusted to the value desired in relation to the delay cable 32. v

The circuit shown in Fig. 6 comprises a second input terminal 107 which is connected to the output of the ampliication stage 11 in the receiver shown in Fig. 3. Through the input terminal 107 all vincorningpulses i. e. signal and synchronisation pulses are thus supplied to the circuit shown in Fig. 6 and more particularly 'to a detector circuit comprising a'diode 108, 'a parallel resistor 109 and an input capacitor 110. When pulses of positive polarity are supplied to input terminal 107 a negative bias isset up across resistorr 109, which bias together with the positive pulses, occurs at the suppressor vgrid of pentode 105. Owing to the negative bias applied to the suppressor grid and the negative bias applied to the'con trol grid, anode current ow's in the anode circuit ofthe pentode only if pulses of positive polarity simultaneously occur at the input terminals 103 and 107.

Besides the aforesaid shaded pulses,l Fig. 7g shows the pulses 'supplied to input terminal L107. yIn the voltage-time diagram of Fig. 7g both -pulse trains supplied are superposed. Only if, in the diagram of Fig. 7g, the pulses `jointly exceed a vparticular #threshold value V02, does an output pulse occur across an anode resistor 111 of pentode 105.

In the circuit arrangement shown in Fig. 6, :these voutput pulses yare supplied to a multivibrator comprising" triodes 112 and 113 and acting as a pulse expander. Such a pulse expander (flip-liep circuit) is known perse. The triodes 112 and 113 are crosswise coupled, i. e. through a coupling capacitor 114 connected between the anode of triode 112 and the control grid of triode 113 and through a voltage divider comprising a resistor 115 which is placed between the anode of triode 113 and the control grid of triode 112 and connected to the negative grid bias lead through a resistor 116. The control grid of triode 113 is connected to the anode voltage lead 118 through a grid resistor 117, so that the triode 113 is conductive in the absence of control pulses. As soon as a pulse of negative polarityappears at the anode resistor 111 of pentode 105, it is impressed through the coupling capacitor 114 on the control grid of triode 113, thus cutting oit triode 113 and rendering triode 112 conductive. After a duration determined inter alia by the values of the capacitor 114 and the resistor 115, the circuit resumes its initial state of equilibrium the triode 113 again becoming conductive and triode 112 being cut off.

The pulses exceeding the threshold value Vez in Fig. 7g thus cause the multivibrator to respond, sov that the lengthened pulses shown in Fig. 7h occur across an anode resistor 119 of the multivibrator, the leading edge of these pulses coinciding with the instants at which the pulses of Fig. 7g exceed the threshold voltage V02.

The lengthened pulses occurring across the anode resistor 119 have a positive polarity and are supplied, through a detector circuit comprising a diode 120, a

cidence mixer stage. With 'the use of the said detector circuit, the 'suppressor grid of pentode I123 acquires -a negative bias su'flcient to out vofi completely the l'anode current ofpento'de 123 in the-interval betweenthe lengthcned pulse's. With 'the use 'of a yvoltage divider comprising resistors '-124, 125, the control grid of pentode 123 is also negatively Abiassed 'such -that I'anode current will flow inthe pentode 123 only Aduring 'the pulses ot' positive polarity supplied thereto. Through a coupling capacitor 126 and input terminal y127 the control grid is connected to a suitable tapping offdelay cable n2'1 (Fig. 3),' the input of 'which is yconnected to the 'output fof pulse regenerator r 27 shown in `Fig. 3. In this-manner substantially noise-free pulses are supplied to the input terminal 127, which pulses have 'been obtained by retardation of the positive pulses vshown in `Fig. 7]C and 'are shown shaded in Fig. 7j. Fig. 7j also shows the vlengthcned pulses supplied to the `'suppressor grid of pentode 123. Only when the pulses supplied by Way of input terminal 127 coincide with the lengthened pulses supplied Jto the suppressor grid of pentode 123, will anode current ow in pentode 123. In Fig. 7j this is indicated oy a threshold value Ver which the superposed pulses must vexceed for causing anode current to flow. The anode currentpulses thus produced'are shown in Fig. 7k.

The anode circuit of pentode 123 comprises a signalfrequencies integrating network 128 across' which occurs kvthe signal voltage transmitted'in the third interval of the 6, the coincidence 'mixer stage comprising the pentode 10S etfects the selection of the pulses occurring in a particular signal interval from the pulses rvreceived in time-multiplex. This selection permits in the channel 'unit shown'in Fig. 6 and after 'the coincidence mixer stage 105 the selected signal pulses to be lengthened to a duration materially exceedin'gvthat of one signal interval. ln this case, substitution ofvtheseflengthened pulses, the leading edges of which exhibit time displacements caused by transmission interference and consequently have a certain noise component, by substantially noise-free ypulses is extremely simple, since the considerable duration of the lengthened pulses permits a considerable phase variation of the substantially noise-free pulses superposed thereon, which is not the case with the receiver shown in Fig. 2. These permissible great phase variations thus permit the tolerance requirements imposed on transmitter and receiver to be materially reduced, so that both the transmitter and receiver become cheaper, in spite of tne necessity of using an additional delay cable and an additional coincidence mixer stage.

It will be obvious that receivers comprising an arrangement according to the invention may also be used for signal transmission by pulse-code modulation with the use of a multi-unit code.

What we claim is:

1. In a time-multiplex pulse-code modulation signaltransmission system wherein successive trains of signal pulses are transmitted, each train having a like number of pulse intervals and being preceded by a synchronization pulse; a receiver for regenerating said transmitted pulses both in form and time of occurrence and for disdilerentiating network in said regenerator and havingv a series of spaced taps each yielding substitution pulses, and a plurality of receiving Ichannels corresponding in number to the number of intervals in a train, each channel including a coincidence mixer, means to supply the received pulses and the substitution pulses derived from a respective tap of said delay network to the input of said mixer, and means to derive the separated and regenerated signal pulses from the output of said mixer.

2. A receiver, as set forth in claim l, further including a controllable phase corrector interposed between said input lter and said limiter, means to mix the input and output pulses of said regenerator to produce a control voltage, and means including a low-pass lilter to apply said control voltage to said phase corrector. 3. In a time-multiplex pulse-code modulation signaltransrnission system wherein successive trains of signal pulses are transmitted, each train having a like number of pulse intervals and being preceded by a synchronization pulse; a receiver for regenerating said transmitted pulses both in form and time of occurrence and for distributing them in cyclical sequence; said receiver comprising a synchronizing pulse selector responsive to the received pulses for separating the synchronization pulses from the trains of pulses, a synchronization pulse regenerator coupled to the output of the selector, a tirst delay network coupled to the output of said regenerator and having a series of spaced taps to yield substitution pulses, a second delay network coupled to the output of said selector and having a series of spaced taps, and a plurality of receiving channels corresponding in number to the number of intervals in a train, each channel including irst and second coincidence mixers7 means to supply the received pulses and the pulses yielded at a respective tap of said second delay network to the input of said second mixer, and means to supply the pulses yielded by scid second mixer and the substitution pulses yielded at a respective tap of said first delay network to the input of said first mixer to produce regenerated signal pulses.

4. A receiver, as set forth in claim 3, wherein said receiving channel further includes a pulse expander interposed between the output of said second mixer and the input of the first mixer.

5. A receiver, as set forth in claim 3, wherein said receiving channel further includes'an amplitude threshold and limiterv circuit for supplying the received pulses to. the input of said second mixer. v

6. A receiver, as set forth in claim 3, wherein said receiving channel further includes an intergrating network coupled to the output of said second mixer to integrate the regenerated signal pulses, 'a reproducer, and a lowpass filter coupling the output of said integrating net- Worky to said reproducer. 7.*n a` time-multiplex pulse-code modulation signaltransmission system wherein successive trains of signal pulses are transmitted, each train having a like number of pulse intervals and being preceded by a synchronization pulse; a receiver for regeneratingsaid transmitted pulses both in form and tirneof occurrence and for distributing them in cyclical sequence, said receiver cornprising means to detect the received pulses, a synchronization pulse selector coupled to said detection means to separate the synchronization pulses from the trains of pulses, a synchronization pulse regenerator coupled to the output of the selector, first and second delay networks each having al series of spaced taps therein, said first network being coupled to the output of said regenerator and yielding substitution pulses at said taps, said second network being coupled to tne output of said selector, and a plurality of receiving channels equal in number to said number of intervals in a train, each channel including rst and second coincidence mixers, means to supply the pulses yielded in the output of said detection means and the pulses emerging from a respective tap on said second network to the input of said second mixer, means to supply the pulses produced by said second mixer and the substitution pulses yielded at a respective tap of said first delay network to the input of said second mixer to produce regenerated signal pulses, and means to integrate said regenerated signal pulses to recover said signal.

p References Cited inthe file of this patent UNITED STATES PATENTS 2,403,561 Smith July 9, 1946 2,414,265 Lawson Ian. 14, 1947 2,449,467 Goodall Sept. 14, 1948 2,537,056 Hoeppner Jan. 9, 1951 2,565,479 Cruikshank Aug. 28, 1951 

